Technical Field
The present disclosure relates to a communications interface apparatus and more specifically, to a communications interface apparatus for Ethernet communications.
Description of the Related Art
In Ethernet architecture, each of devices connected to a network uses Ethernet data that has the structure including a 48-bit MAC (media access control) address, its address, and a CRC code for detecting data and err. The device communicates data among them by using such addresses.
A BNC cable, a UTP cable and a STP cable are used as transmission media, and devices such as a hub, switched and repeaters are used to connect the devices.
The Ethernet uses the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) technology. This technology allows a number of devices connected to Ethernet to share a single transmission medium.
FIG. 1 shows an existing communications interface apparatus.
Referring to FIG. 1, the communications interface apparatus includes a port 10, a physical layer interface 20, a media access control (MAC) layer interface 30, and a FIFO (First-In First-Out) 40.
The port 10 may be an Ethernet port and may receive a signal from an external device via a cable.
The physical layer interface 20 may process data transmitted from the port 10 via the cable to output it.
The MAC layer interface 30 may receive the data from the physical layer interface 20 to recognize fields in the data and may process and store the data conforming to the Ethernet protocol.
The FIFO 40 transmits the data stored in the MAC interface 30 to an upper layer via a bus.
FIG. 2 shows the data field format of Ethernet data.
The Ethernet data includes a preamble, a DA (Destination Address) field, a SA (Source Address) field, a type/length field, a data/payload field, a FCS (Frame Check Sequence, CRC) field.
An upper layer checks data stored in the MAC layer interface 30, processes transmit data to be transmitted to an external device and transmits it to the MAC interface 30.
Specifically, if a host attempts to transmit data, the host (transmit host) detects a signal in the network, determines whether data can be transmitted, and begins transmission if possible.
If there is collision between data, the transmit host broadcasts a jam signal. A host corresponding to the destination of the data (receive host) checks the value of the data transmitted from the transmit host and determines whether the data is defective.
The receive host transmits the received data to an upper layer if there is no defect in the CRC value of the data, and discards the received data if there is a defect in the CRC value of the data.
If there is collision between data, the transmit host retransmits the data after a random time period. The retransmission is performed after a random time period instead of a fixed time period, because collision may occur again after a fixed time period and thus the collision can be detected.
According to such Ethernet communications method, however, transmit data is created after the data received in the upper layer has been processed. Then, the transmit data is transmitted from the receive host to the transmit host. Accordingly, there is a problem in that it takes long time for the transmit data to be transmitted from the receive host to the transmit host.